deep
Extending far down from the surface; profound or intense.
Etymology
Modern English deep comes from Old English dēop "profound, vast, extending far down," from Proto-Germanic *deupaz, from PIE *dʰewb- meaning "deep, hollow." The same root produced Lithuanian dubùs "deep, hollow" and Welsh dwfn "deep" (from Brythonic *dubnos). The Celtic connection is particularly interesting: the ancient Gaulish word dubno- "deep, world" appears in place names across Europe, including the Danube River (from Celtic *Dānuvius, possibly "deep river") and Dublin (Dubh Linn, "black pool"). The Germanic family includes German tief, Dutch diep, and Old Norse djúpr. Within English, dip may be related through a variant form. The metaphorical extension from physical depth to intellectual profundity — "a deep thought" — was already present in Old English, suggesting this transfer is ancient.
The Journey: *dʰewb- → deep
*dʰewb-
*deupaz
dēop
deep, depe
deep
Cognates Across Languages
These words in other languages descend from the same PIE root *dʰewb-. They are not borrowings but independent inheritances from a common ancestor.
| Language | Word | Meaning |
|---|---|---|
| Lithuanian | dubùs | deep, hollow |
| Welsh | dwfn | deep |
| German | tief | deep |
| Old Norse | djúpr | deep |
| Gaulish | dubno- | deep, world |
Did You Know?
The name Dublin comes from the same PIE root as English deep. Dublin derives from Old Irish Dubh Linn "black pool" — dubh from Celtic *dubno- "deep," a cousin of English deep. The Danube River may also carry this root, from a Celtic name meaning "the deep one."